1. Field of the Invention
This invention relates to a single ply roofing membrane having a top layer and a bottom layer for covering industrial and commercial flat and pitched roofs. More particularly, the invention relates to a single ply reinforced roofing membrane in which the bottom layer is embossed to improve roll blocking without sacrificing the heat seaming performance of the roofing membrane.
2. Reported Developments
Single ply roofing membranes to cover flat and pitched roofs are known in the art of commercial roofing membranes. Some membranes comprise bottom and top polyolefin-based sheets with a fiber reinforcement scrim sandwiched between the sheets. To promote adhesion between the scrim and the polyolefin sheets, a highly flowable, functional-polyolefin is incorporated into one or both sheets as disclosed in U.S. Pat. No. 6,544,909.
Other membranes of the prior art consist of materials based on atactic polypropylene (APP) modified bitumen. Still other membranes consist primarily of materials based on styrene-butadiene-styrene (SBS) modified bitumen. Attachment of these membranes to underlying roof decks are accomplished with adhesives and/or screws. To adhere one membrane to another membrane to render the roof covering waterproof, the selvage edge of one membrane is overlapped with the selvage edge of the next membrane. A torch is then used to soften the membranes at their overlapped portions to achieve a seam sufficient to withstand weather conditions.
U.S. Pat. No. 6,134,856 discloses a roll roof membrane , and a method for its preparation, which obviates the use of a torch to achieve a seam between the overlapped portions of the membranes. The roof membrane comprises a support sheet having bonded on the top and bottom surfaces thereof layers comprising APP modified bitumen, a first selvage edge disposed in the top APP modified bitumen layer along one side of the membrane, a second selvage edge disposed in the bottom APP modified bitumen layer along the opposite side of the membrane, and wherein each of the selvage edges have a series of embossed ridges and valleys adopted to accept adhesives, the valleys extending substantially through the APP modified bitumen layers to the support sheet.
The method of preparing the roll roof membrane includes the steps of: a roll of support sheet is unwound and passed through an accumulator; the unwound sheet is dip coated by immersion in a coating vat containing molten compounded APP, asphalt, and one or more fillers and fire retardants; while the coatings are in a molten state, the selvage edges on opposite sides and opposite surfaces of the membrane are contacted with top side embosser and bottom side embosser; the APP modified bitumen layers are cooled and solidified by floating the membrane in a water bath and the membrane is wound into a roll. A suitable liquid parting agent, such as a coconut oil, can be added to the bottom surface of the membrane to reduce the tendency for the membrane to stick during winding and subsequent handling.
We have observed that roll blocking tends to occur with single ply membranes of the prior art. As the membranes are produced, they are wound into rolls, stored in roll configurations and delivered to the site of installation. Since the membrane is smooth, portions thereof tend to stick and adhere to each other thereby hindering the unwinding process. Embossment of selvage edges on opposite sides and opposite surfaces of the membrane does not appear to solve the roll blocking problem: while the embossed portions of the membrane easily unwind, the remaining portions constituting the majority of the surface area tend to stick and adhere to each other.
We have now discovered that the roll blocking problem can be greatly reduced by the complete embossment of the bottom layer of the single ply membrane.